Cyclohexanediamine is an industrially important compound to be used as a raw material for e.g., epoxy curing agents and polyurethanes. A cyclohexanediamine has two isomers, i.e., a cis isomer and a trans isomer, derived from the cyclohexane ring.
Trans-1,4-bis(isocyanatocyclohexane) obtained from a trans isomer of 1,4-cyclohexanediamine is particularly useful as a polyurethane material and a cis isomer of 1,4-cyclohexanediamine, which can liquefy, is particularly useful as a curing agent for epoxy resins.
For these reasons, it is extremely important to control the isomer ratio of a cyclohexanediamine. As a method for controlling the isomer ratio of a cyclohexanediamine, various methods have been proposed.
As a method for controlling an isomer ratio, for example, a method of isomerizing 1,4-cyclohexanediamine in the presence of a noble metal catalyst under high temperature and high pressure conditions is known (Patent Literature 1, Patent Literature 2).
Another method is disclosed, in which p-phenylenediamine is nuclear-hydrogenated; and from the resultant mixture of a cis isomer and trans isomer of 1,4-cyclohexanediamine, the trans isomer is separated by e.g., crystallization; and the filtrate rich in the cis isomer is fed back (for recycling) to an isomerization step (Patent Literature 1, Patent Literature 3).